/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
    TreeNode* _buildTree(vector<int>& preorder, vector<int>& inorder,int &prei,int inbegin,int inend)
    {
        if(inbegin > inend)
        {
            return nullptr;
        }
        TreeNode* root = new TreeNode(preorder[prei]);
        int rooti = inbegin;
        while(rooti <= inend)
        {
        if(preorder[prei] == inorder[rooti])
                break;
        else rooti++;
        }
    
        prei++;
        root->left = _buildTree(preorder,inorder,prei,inbegin,rooti-1);
        root->right = _buildTree(preorder,inorder,prei,rooti+1,inend);
        return root;
    }
public:
    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
        int prei = 0;
        return _buildTree(preorder,inorder,prei,0,inorder.size()-1);
    }
};
